Appendix D Tables and Figures

Transcription

1 Appendix D Tables and Figures

2 PC-HYDRO User Guide V5 Figure D-1. Hydrologic Soil-Cover Complexes and their Associated SCS Curve Numbers D-1

3 Figure D-2. Aerial Reduction for Watersheds Larger Than Ten Square Miles (modification of Weather Bureau Technical Paper 40) D-2

4 Table D-1. Summary of SCS Curve Numbers for Desert Brush Hydrologic Soil Types Vegetative Cover Density 10% 20% 30% 40% Types A and B Type C Type D Table D-2. Summary of SCS Curve Numbers for Urban Lawns Hydrologic Soil Types Vegetative Cover Density Poor < 30% Coverage Average 30% to 60% Coverage Excellent > 60% Coverage Types A and B Type C Type D D-3

5 Table D-3. Summary of Approximate Impervious Cover Percentages for Various Land Development Types Development Type Impervious Cover Percentage Minimum Average Maximum Rural and Suburban: a. Less than 1 house/acre 5 % 10 % 20 % b. 1 house/acre 15 % 20 % 25 % c. 2 houses/acre 25 % 30 % 35 % Light to Moderate Urbanization: a. 3 houses/acre 30 % 35 % 40 % b. 4 houses/acre (detached) 35 % 40 % 45 % c. 5 houses/acre (detached) 45 % 50 % 55 % Highly Urbanized: a. Multiple Dwellings, 4 units/acre or more 50 % 65 % 90 % c. Light Industrial and Commercial 50 % 65 %-75% 80 % d. Heavy Industrial and Commercial 80 % 85 %-95 % 100% D-4

6 Table D-4. Values of R1 and R2 for a Selected Range of Curve Numbers from 95 to 60 CN R1 R2 CN R1 R D-5

7 Table D-5 Basin Factors for Undeveloped or Developed Areas with No Drainage Improvements Watershed Type Mean (ft/ft) Slope (minimum) (normal) (maximum) Mountain 1 > Foothills to Valley 3 < to Table D-6 Basin Factors for Developed Areas with Drainage Improvements (excluding areas of shallow sheet flow) Watershed Type Development Density (minimum) (normal) (maximum) Suburban-Foothills 4 Suburban-Valley 4 Suburban-Foothills 4 < 1 house/acre < 1 house/acre 1-2 houses/acre to Suburban-Valley 4 Light to Moderate Urban 5 Highly Urbanized 6 Commercial Industrial 7 and 1-2 houses/acre 3-5 houses/acre (detached) Apartments to Light Commercial to Heavy Commercial and Industrial D-6

8 Table D-7 Basin Factors for Shallow Sheetflow and Overland Flow Areas (Restricted Use) Watershed Type Watershed Condition nb Paved 8 all Paved and Natural 8 Natural 8 Suburban Light Urban Moderately Urban Rough Normal Smooth Mountain Areas are mostly undeveloped and are relatively rugged, narrow, and have sharp edges. Similarly, these areas often have relatively steep canyons through which watercourses meander around sharp bends, over large boulders, and through frequent debris obstructions. The ground cover in mountain areas, excluding occasional small areas with rock outcrops, usually includes numerous trees and considerable underbrush. In addition, there are no significant drainage improvements in undeveloped Mountain Areas. 2. Foothill Areas mostly undeveloped, and often have rolling terrain with rounded ridges and moderate side slopes. Watercourses typically follow relatively straight, unimproved channels, with some boulders and occasional lodged debris. Ground cover usually includes scattered brush and grasses. In addition, there are no significant drainage improvements in undeveloped Foothill Areas. 3. Valley Areas are mostly undeveloped, and often have comparatively uniform, gentle slopes, as well as surface characteristics in which well defined natural channelization does not occur. Ground cover usually includes grasses, small shrubs, cacti, and similar desert vegetation. In addition, there are no significant drainage improvements in undeveloped Valley Areas. 4. Suburban Areas have low- to moderate-density developments comprised of detached family homes or light commercial and industrial uses, and often have relatively uniform, gently slopes with only some watercourses that are either improved or follow paved D-7

9 streets. 5. Light to Moderate Urban Areas usually have multiple residential dwellings, or moderate industrial and light commercial uses. These areas are similar to Suburban Areas, but with most watercourses being either improved or following paved streets. 6. Highly Urbanized Areas are similar to Light to Moderate Urban Areas, but with a large percentage of the area impervious, and virtually all watercourses are either improved or follow paved streets. 7. Commercial Areas are similar to Highly Urbanized area, but less than 15% of the area remains pervious. 8. Shallow Sheetflow Areas and Overland Flow Areas (restricted use). Shallow Sheetflow Areas typically have extremely uniform, flat slopes with no natural or constructed channel. Surface flows do not exceed 0.5 feet in depth. Overland flow occurs at the upper reaches of a watershed where the flow is not channelized over relatively short distances. Along natural surfaces, ground cover may consist of cultivated crops or substantial growths of grass and fairly dense, small shrubs, cacti or similar desert vegetation. Generally, no drainage improvements exist in the area. The use of Basin Factors for Shallow Sheetflow Areas is restricted. The user shall obtain approval from the District prior to applying the Shallow Sheetflow Basin Factors listed in Table 4.3. to any watershed or portions of a watershed. Furthermore, the user shall provide written and photographic justification for selecting these Sheetflow Basin Factors with any subsequent drainage analysis submitted to the District for review or approval. Basin Factors shall be selected for future, fully developed conditions, based on the best available information regarding future land use potential. When calculating flood peaks using PC- HYDRO, the user shall describe this future land use, and the published source from which this information or projection was obtained. Basin Factors for watersheds or subwatersheds that are not homogeneous shall be identified, and the proportion of each watershed and development type quantified. From this information, an area-weighed average Basin Factor shall be calculated and then used. D-8

10 Table D-8 Approximate Ratios of Lesser Magnitude Floods to the 100-Year Flood Watershed Development 2-Year 10-Year 25-Year 50-Year Rural Suburban Moderately Urban Highly Urban D-9